oci: fix segfault when cgroup cannot be configured
oci: fix segfault when cgroup cannot be configured

avoid a segfault if the cgroup hierarchy could not be configured.

It happens every time with rootless mode as we cannot configure
cgroups, but it is not restricted to rootless.

Closes: https://github.com/cri-o/cri-o/issues/2205

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

kubernetes-incubator/cri-o,kubernetes-incubator/cri-o,mikebrow/cri-o,rhatdan/cri-o,rhatdan/cri-o,kubernetes-incubator/ocid,kubernetes-incubator/ocid,kubernetes-incubator/cri-o,nalind/cri-o,kubernetes-incubator/cri-o,mikebrow/cri-o,rhatdan/cri-o,kubernetes-incubator/ocid,mikebrow/cri-o,mikebrow/cri-o,nalind/cri-o,rhatdan/cri-o,nalind/cri-o